1. Field of the Invention
This invention relates to a magnetic toner used in recording processes such as electrophotography, electrostatic recording, electrostatic printing and so forth. This invention also relates to an image forming method making use of the magnetic toner.
2. Related Background Art
A number of methods are conventionally known as methods for electrophotography. In general, copies or prints are obtained by forming an electrostatic latent image on an electrostatic latent image bearing member (hereinafter also “photosensitive member”) by utilizing a photoconductive material and by various means, subsequently developing the latent image by the use of a toner to form a toner image as a visible image, transferring the toner image to a recording medium such as paper as occasion calls, and then fixing the toner image to the recording medium by the action of heat and/or pressure. Apparatus for such image forming include copying machines and printers.
In recent years, these printers or copying machines have been advanced from analogue machines to digital machines, and it is strongly required to have faithful reproducibility of latent images and high resolution and at the same time to reduce power consumption in their use.
Here, taking note of printers, for example, the proportion of power consumption in the fixing step is fairly large in respect to the total power consumption, and hence the power consumption may increase with a rise in fixing temperature. High fixing temperature may also cause problems such as curl of image-printed paper after fixing. Accordingly, there is a great desire for lowering fixing temperature. It is further sought to deal with various recording materials, where toners are required to have good fixing performance in a broad temperature range.
To cope with this, until now, many studies have been made on how to fix toners at lower temperature. For example, as disclosed in Japanese Patent Application Laid-open No. H5-297630, it is reported that by controlling molecular weight distribution and THF (tetrahydrofuran)-insoluble matter, low-temperature fixing performance is improved and both low-temperature fixing performance and high-temperature anti-offset properties are achieved.
Many studies are also made on low-softening substances to be added to toners. A technique is proposed in which particle surfaces of a magnetic powder is treated with a low-softening substance to improve the dispersibility of the magnetic powder in toner and also to improve fixing performance (e.g., Japanese Patent Applications Laid-open No. H9-319137, No. H1-259369 and No. H1-259372).
However, even with use of such a magnetic powder, there is still room for improvement in both low-temperature fixing performance and high-temperature anti-offset properties, and the improvement in fixing performance has still been insufficient.